The present invention relates to a fuel injector system having a fuel injection valve, which is mounted in an internal-combustion engine to control the amount of fuel supplied to the engine, and to a method of controlling the fuel injection valve.
In general, a fuel injection valve comprises a fuel injection orifice, a valve seat disposed in the vicinity of the fuel injection orifice, a valve body slidably supported in an axial direction at the position facing the valve seat, and a spring. The spring generates a force that presses the valve body in the direction of and into contact with the valve seat so as to close the valve orifice. Thus, while the valve seat and the valve body are kept in contact by the spring force, that is to say, in the closed status of the valve, since the fuel passageway through the fuel injection orifice is closed, fuel is not injected from the fuel injection valve.
The fuel injection valve also has a magnetic circuit and coil assembly for driving the valve body. The application of a current to the coil assembly exerts a magnetic attraction force on the valve body, causing the valve body to slide in an axial direction and move away from the valve seat, thereby to open the fuel passageway through the fuel injection orifice. At this time, since the fuel passageway is opened, fuel is injected from the fuel injection valve.
In the operation of such a fuel injection valve, the amount of fuel supplied can be controlled by adjusting the time during which the open status of the valve is maintained. To precisely control the amount of fuel supplied to the internal-combustion engine, it is necessary to reduce the minimum amount of injection that represents the minimal value of the controllable amounts of fuel capable of being supplied. To achieve such a reduction, the valve body needs to be opened at high speed, and, for this purpose, the supply of current to the coil assembly needs to be rapidly started.
A patent document 1 (Japanese Application Patent Laid-Open Publication No. Hei 08-45735) exemplifies the conventional technology related to the above-described fuel injection valve operation.
According to the patent document 1, in an electromagnetic load-driving method that uses at least one series circuit, which includes a load and a changeover means, changeover control is provided so that supply of a current to the coil assembly can be rapidly started by setting a small resultant inductance for a first time interval, in other words, for valve opening, and a large resultant inductance is then set for a second time interval, which represents the valve-opening retention duration, following the above-mentioned first time interval.